Saw chain



V United "States Patent [56] References Cited UNITEDSTATES PATENTS 5/1918 Fisher........................... 3,283,789 11/1966 Si1von.......

[72] Inventor John W. Oehrli Pacific Palisades, California 743,843

July 10, 1968 Nov. 24, 1970 Lillian M.

[21] Appl. No. [22] Filed 3,329,183 7/1967 Robinson..................:.: Primary ExaminerD0nald R. Schran Attorney-Forrest .l. Lilly [45] Patented [73] Assignee Oehrli sole legaiee and devisee under the Will of John W. Oehrli, deceased D m mm m6 m In n a 1 m WC S. PWM A6 Mk 8 U IF. 1 l 1] 4 2 0 5 5 55 l I [l Pafentd Nov, 24, 1970 Sheet L of 2 I NVENT OR.

firroavw; y

, Patented Nov. 24, 1970 Sheet 3 of 2 Joy/v W OKHPA/ INVENT OR.

firm/W5 s SAW CHAIN FIELDOF THE INVENTION This invention relates: generally to saw chain, and more particularly to improvements insaw chain of a type in which successive cutter-carrying side links are furnished at their proximate ends with interengaging formations intended to stabilize the chain by preventing the cutter-carrying side links from moving or tilting substantially outward from their predetermined normal path at any point in their course of travel. Thereby, a number of advantages are promised, as is well known inthe art.

BACKGROUND OF THE INVENTION Saw chainof the type to which the present invention appertains is driven about the peripheral edge of a chain saw bar by a drive sprocket adjacent the rear end of the bar. The chain may be made upof the cutter-carrying side links, alternating with center drive links, the latter having lugs or roots engaged by the sprocket. In another but less common type, the side links rather than the center links are sprocket driven, and the present invention is applicable to either arrangement. The first-mentionedfform, with the center links driven, will be chosen for present illustrative purposes, but without implied limitation. With this first form particularly inmind, the side links may ride around the drive sprocket on circular rims or rotatable discs concentric with the sprocket, or otherwise. The chain runs along one edge of the saw bar, goes off the rearward end thereof to and around the'drive sprocket, together with whatever rim, disc, or guide means, may be provided, and

then onto the rearward end of "the opposite edge of the saw barj In the course ofitravel along the working edge of the saw bar, the side links, with their cutters in engagement with the wood, tend to rock up about their rearward pivots on the chain, as is known. Also, in going around the sprocket, the

. cutter links may behave erratically, tending to kickup about their rearward pivots. These actions give the chain an erratic behavior, involving changes in tension, and consequent vibration, wear, and fatigue. Moreover, when sharpening devices are used on the chain passing over the rearward sprocket, such erratic behavior of the cutter links interferes seriously with sharpening. Highly uniform sharpening is prevented, as well as the attainment of a good, uniform clearance angle.

Efforts havebeen made to cure these problems, including use, at the trailing end of a given cutter link, of a tailpiece to bear against-and prevent kickup of the front end of the followingcutterlinkQSome of these devices may have secured a degree of control over the cutter link along the straight edges of the bar, but not around the sprocket. Some also have the undesired characteristic that they prevent the chain from being bent back from a straight line, introducing a problem in compact packaging for shipment.

Another proposal has been to furnish the side links with leading and trailing extensions formed with gear sectors formed about their corresponding pivots in the chain, the gear sector on the trailing end of .a side link meshing with the gear sector on the leading end of the following side link. The avowed purpose here is to prevent pivotal movement of a side link with respect to an adjacent center link without equivalent link pivotally connected .to the same center link. This very characterizing feature,.however, introduces an apparently unrecognizedadded problem, in that, for example, as each side link goes tangentially off the sprocket, it necessarily pivots outwardly on the succeeding center link to reduce its angle relative thereto. The gear action then tends to cause the succeeding side link to pivot oppositely, tending to urge its rearward end to lift off the sprocket. Under the prevailing forces, this succeeding side link, instead, maintains its seat on the sprocket, the center link pivots outwardly, and the tangentially departing side link, reducing its angle relative to the center link, is forced to rise off the sprocket by a troublesome distance, e.g., about .085 inch (inclusive of the approximately .028 inch rise that results from the conventional arcuate depression in the bottom edges of the side links). The rise owing tothe intergearing alone thus is about .057 inch, and the total rise is sufficient to cause a large amount of pulsating tension and vibration, not withstanding that the chain tends to be a trifle slack just beyond thedrive sprocket. A similar or equivalent phenomenon, but of more serious consequence, occurs as each geared side link goes onto the sprocket. In this case, as each side link moves tangentially onto the sprocket, the preceding link will-be pivoting inwardly to turn about the sprocket, and thus to increase its angle relative to the firstmentioned link. The preceding link is drawn tautly against the sprocket, by reason of the drive effort, and the gear action from the preceding link'through the interconnecting center link to the side link moving tangentially onto the sprocket then lifts the latter link off the sprocket, again by .057 inch added t1 the already existing .028 inch, or by a total of .085 inch. This rise of the side links just going onto the sprocket is more serious than the rise of the side links in leaving the sprocket, since the chain is taut where it goes onto the'drive sprocket, and a rise of the magnitude indicated will create a periodic tension of a very disturbing magnitude, causing serious vibration. The same action, of course, takes place at both ends of the bar. These conditions thus result in periodic tensioning of the chain and magnitudes sufficient to cause serious vibration, with its known consequences.

The principal purpose of the present invention, accordingly, is to provide a saw chain of the broad class discussed in the immediately foregoing passages, but which abandons the principle of gearing of successive side links together, with the enforced consequence that each pivotal movement of a side link acts through the adjacent center link to cause an equal and opposite pivotal movement on the next adjacent side link, and which substitutes therefore a restraining means configuration on the trailing end of each side link, interacting with a configuration on the leading end of the following link to impose a restraint on the latter against outward pivotal action, both on the straight edge of the bar, and around the sprocket.

' BRIEF SUMMARY OF THE INVENTION The invention uses, in present illustrative examples, alternating cutter-carrying side links and center drive links pivoted end-to-end, and has rearward extensions from the trailing ends of the side links interengaging with forward extensions projecting from the leading ends of the side links. These interengaging configurations are shaped to slide or ride on one another as the chain pursues its straight or substantially straight runs along the cutting edges of the saw bar, as well as around the curved runs about the sprockets at the ends of the longitudinal edges of the saw bar. When the side links are on the straight runs, a formation on the trailing end extension of each side link overlies and engages a formation on'a leading end extension of the succeeding side link, and thus restrains the front end of the succeeding link against cooking up about its rear pivot as a consequence of penetration into the wood, or from any other cause. Since the trailing end of each side link is forceably held down by its own cutters engagement with the wood, it is thereby entirely capable of restraining the succeeding side link from cocking up. Then. as the side links go onto the sprockets, and/or onto any end guide means that may be provided, the side links swing apart on their pivotal connections to the center links, and the interengaging restraining formations momentarily part from one another. At this position, I there is no tendency for the momentarily released link to tilt out, since generally, the chain is not cutting in this region, and has not yet engaged any sharpening device that may be used. The restraining formations immediately,

' however, move to new positions relative to one another, in

tinuous through the curved guide path around the sprocket and off the sprocket and onto the longitudinal edge of the saw bar. Interactions between successive side links through the intervening center link, such that the side links are constrained to equal and opposite pivotal movements relative to the center links, with consequent large rises of the side links in the regions where these links go onto and leave the sprocket are avoided or with some forms of the invention, ameliorated sufficiently to eliminate the problem for all practical purposes. At the point where the side links go off the sprocket, there is, with kinematically ideal forms of the invention, no rise of the side links at all; and with certain other embodiments of the invention, the rise" is held so low that, in view of the normal slack in the chain just past the drive sprocket, no problem arises. At the point where the side links are going onto the sprocket, where chain tension is high, the rise" of the side links is eliminated entirely since at this point, the interengaging formations between successive side links have separated from one another. The problem of chain vibration from the source mentioned is thus fully met.

The maintenance of the side cutter links in their predetermined curved path of travel about the sprocket is of particular importance when sharpening the cutters on their outer surfaces in the course of such travel to provide a clearance angle. It will be appreciated that if the cutter links tilt outward about their rearward pivots in the course of such travel, the outer surfaces of the cutters will tend to be ground without appreciable clearance angle; but if held steadily against such action, as results from the practice of the invention, a good clearance angle can be obtained. It will be further understood that the steadiness of travel of the cutters in the sharpening area is also of importance with any form of sharpening practice which operates on the cutters while traveling about the sprocket.

DESCRIPTION OF THE DRAWINGS Illustrative embodiments of the invention are shown in the accompanying drawings, in which:

FIG. I is a side elevational view, partially in section, and to double scale, showing a preferred form of saw chain in accordance with the invention, and showing such chain as it goes around a'conventional rim drive sprocket;

FIG. 2 is a view similar to FIG. 1 but showing another position of the sprocket and chain;

FIG. 3 is an enlarged detail of the leading end portion of a side link in accordance with the invention;

FIG. 4 is an elevational view, partly in section, to double scale, showing a modified form of the invention making ap- DESCRIPTION OF PREFERRED EMBODIMENT FIGS. 1 and 2 of the drawings show a kinematically ideal embodiment of the invention. The saw chain has alternating pairs of pivotally connected side links 14 and center links 16, the latter of a conventional type, formed with drive lugs or roots 17 which ride in the usual peripheral groove in the saw bar, not shown, and which engage in the pockets 18 between the teeth 19 of a rim sprocket 20. A rim sprocket is here shown, illustratively, but without implied limitation thereto, as of a conventional seven-tooth type, provided with circular rims or discs 21, on opposite sides of the pockets 1% to support the side links 14 of the chain on both sides of the center links 16. The bottom edges of the side links are formed with arcuate depressions 14a to fit the rims or discs 21. The side links 14 are connected to the center links by pivots 22, and in the specific embodiment here shown, the center-to-ccnter spacing of the two pivots of each pair of side links 14 is the presently conventional .404 inch, with the center-to-center spacing of the two pivots of the center links the same, though not necessarily so. It will be seen that, when the side and center links are on the sprocket, the centerlines of successive links, from pivot to pivot, are at exterior acute angles and to one another.

The side links bear cutters, which may, insofar as the present invention is concerned, be either scratcher type cutters or of the router or chisel type. For simplicity of illustration, I here show conventional scratcher type cutters, comprising, in repeating order, on successive side links, a lefthand side cutter 14a, a left-hand raker 14b, a right-hand side cutter 14c, and a right-hand raker 14d. The upper edges of these cutters can be sharpened with a clearance angle c using a concave faced sharpener disc engaging the tops of the cutters within the back arc indicated in FIG. I (see my U.S. Pat. No. 3,260,287). Other methods of sharpening are of course in contemplation.

The trailing end of each side link 14 has a rearward extension 25 cooperating with a leading end extension 26 on the leading end of the following side link 14, and these configurations are such that the trailing parts 25 restrain the leading parts 26 to prevent the links from tilting outward and back, either along the longitudinal edges of the saw bar, or in going around the sprocket, and from the sprocket ontothe saw bar.

The leading end part 26 has, in the embodiment of FIGS. 1 and 2, a convex arcuate surface or seat 30, struck on an are at a radius R about the center of the forward pivot 22 and extending substantially from a point a little short of the outermost edge 31 of the link to somewhat past the longitudinal centerline A-A of the link determined by the centers of the pivots 22. The arcuate seat 30 preferably merges tangentially, near the top, with a straight 30 surface 30a that intersects the top edge 31 of the link 14 (FIG. 3).

The trailing end part 25 of the preceding side link has, extending inwardly and under from its outermost edge, a coacting concave arcuate restraining surface 34, of slightly shorter radius R and struck about a center 0, located on the longitudinal centerline or'axis A-A', but a little short of the center of the front pivot 22 of the following link 14 when the two links 14 are in longitudinal straight line alinement (as are the two links 14 leaving the sprocket in FIG. 1). See the enlarged fragmentary detail in FIG. 3. The distance from the center of pivot 22 to the center 0 plus the length of radius R exceeds the radius R by a small amount, so that the arcuate surfaces 30 and 34 meet at the top, but have a clearance at the axis A-A'. It will be seen, then, that when the links 14 are longitudinally alined along the straight line A-A', the upper portion of the surface 34 engages the upper portion of the arcuate seating surface 30, and so holds the front end of the following link 14 down against any tendency for this link to kickup up about its rear pivot.

The lower portion of the arcuate seating surface 30 on the head end of each link 14, inward of the longitudinal centerline A-A' of the link, forms the rear flank of a notch 36, whose bottom 37 merges with a convex front flank 38 of the notch 36. The convex flank 38 is preferably on an arc struck about the center of therear pivot 22 of the preceding side link 14 when the links 14 are on the rim of the sprocket 20, and angularly related by the angle 20:. The flank 38 is formed on a toe 40 which extends upwardly and forwardly from the bottom portion of the link 14, as shown.

The arcuate surface 34 on the rearward extension 25 of each side link 14 extends downwardly to the centerline A-A' of the link, forming the outer flank of a toe 42, in back of which is a deep notch 43 adapted to receive the toe 40 of the following link 14. The notch surface 44, which forms a flank of the toe 42 as well as the outer defining surface of the notch 43, is formed preferably on an arc struck about the center of the rear pivot 22 of the link, and the surfaces 38 and 44 accordingly are shaped to slide on one another as the link 14 at the top center, in FIG. 1, progresses toward the right, as to the position shown in FIG. 2, i.e., as the successive links 14 reduce their maximum angle 20: relative to one another to a.

The top center link 14 and the precedinglink 14 show the relative position of the links in traveling along the straight edge of the saw bar, not shown; and it will be seen that the stop or restraining surface 34 of the preceding link 14 engages and bears down on thesurface 30 of the following link, so as to hold the latter down on the saw bar, and against tilting out on its rearward pivot; The holding pressure exerted by the stop 34 of the preceding link 14, particularly during cutting, is great because of the downward pressure exerted on the rearward end of the link by its cutter in engagement with the wood.

In going onto the sprocket, at the bottom, the link 14 goes first into the relative'position shown at the bottom in FIG. 1, as the preceding link-14 tilts upward onto the sprocket rim 20. It will be seen thatin this position, the links 14 in question have been tilted so that the two normally coacting end portions 25 and 26 thereof are entirely out of engagement. Thus, neither influences the position of the other relative to sprocket rim 20, and the chainis drawn tangentially onto the sprocket rim in normal fashion. y I

As the links then progress to the position shown at the bottom in FIG. 2, the toe 40 on the link 14, then at bottom center, engages a stop point or element 44a on the arcuate surface 44 of the preceding link 14..The two arcuate surfaces 38 and 44 are thus brought into engagement, so as-to hold down the front end of the following link, and will not move on or relative to one another until the upper center position on the sprocket is approached. Thus, the successive links 14 move around from a position on the bottom portion of the sprocket rim 20 to the position represented at the top in 'FIG. 1 without further movement of the links relative to one another. Beyondthe position at the top, FlG. 1", and on to the succeeding position at the top, FIG. '2', however, the link 14 immediatelyfollowing the top center link 14 (FIG. I) rocks clockwise relative to the latter,*causing the arcuate surface 38 to slide on the arcuate surface 44, and the arcuate seat 30 on the leading end of the trailing link 14 to become engaged and thereafter held down by the arcuate stop surface 34 on the trailing end of the leading link 14. The links thus move into the position shown at the top center, in FIG. 2, where the arcuate surface 34 has engaged the arcuate'surface 30, with the arcuate surfaces 38 and 44 in contact. Beyond this position, the arcuate surface 30 on the following link 14 rotates further on the arcuate surface 34 onthe leading link 14, and by the time the position at the top in FIG. 1 is reached, where two successive links 14 are shown in rectilinear alignment, the two surfaces '38 and 44 have parted entirely from one another, whereas the surface 34 of the preceding link 14 is in holddown engagement with the surface 30 of the immediately following link 14.

It should be clear from the foregoing that when the links are in rectilinear alignment, as along the straight edges of the saw bar, each link 14 interacts on the link 14 following it to hold it against outward tilting on its rearward pivot. Moreover, in

leading and trailing links reduce their angle to one another, as

be no reactionwhatsoever from each preceding link to its immediately following link, and therefore the following links go smoothly and tangentially onto the sprocket without kickup and ensuing tensioning pulses. It will be clear that this clearance and freedom is considerable, and allows substantial leeway for design modification. Some minor modifications within this leeway are indeed desirable, even though they may result in slight to moderate rise of the links 14 as they leave the top of the sprocket, where such rise is not conducive to problem behavior, as presently to be set forth.

Reference is next directed to FIGS. 4 and 5 showing a modification of the chain of the preceding FIGS., the chain links in this instance resembling those of the preceding embodiment in substantially all material respects, with the exception of certain minor modifications made for the purpose of increased ruggedness and improved ease of fabrication. For the sake of convenience, components of the saw chain and sprocket in FIGS. 4 and 5 corresponding to the first described embodiment will be identified by corresponding reference numerals, but with addition of primes in the case of FIGS. 4 and 5. A rim type sprocket 20' is again illustrated, as well as a chain 10 having center drive links 16' connected by pivots 22 to cutter-carrying side links 14.

It will be seen that the chain of FIGS. 4 and 5 has interengaging seating surfaces 30 and 34', the same as that of FIGS. 1 and 2 and also has a notch36', a toe 40', another toe 42', and a notch 43', all corresponding to similar elements in FIGS. 1 and 2. The shapings of these elements, however, are somewhat modified, in the case of FIGS. 4 and S, for increased ruggedness and ease of manufacture, in ways and for reasons that will be-clear to those skilled in the art by inspection of FIGS. 4 and 5. Thus, the notch 36' is more shallow, and drops only slightly below the centerline of the link. The notch 43' is also more shallow, and in the case of FIGS. 4 and 5, is bounded by a substantially straight angular flank 44. The flank 38' of the toe 40' engages the flank of the toe 42' for a substantial distance in the position at-top center in FIG. 5. where the leading link 14 is moving substantially tangentially off the sprocket. Where both the following and leading links 14' are fully on the sprocket, the toe 40' engages the flank 44' near the tip of the former, as clearly shown in the drawings; and in such'positiom-the leading link is clearly holding the front end of the following link down on the sprocket. As the the leading link goes tangentially off the sprocket, the toe 40' rides up the flank 44 to the position shown at the top in FIG.

5. Thereafter, as the following link 14' moves upwardly and going around'the sprocket 20, the interengagements between successive links 14, at the surfaces 38 and 44, constrain the links to follow their predetermined guide path, and do this with high precision, With this condition maintained, cutter angles can be ground, or edges sharpened, in the back 180 arc of the chain on the sprocket, without variances and without erratic results. In particular, it becomes possible to grind a mally engaging stop or restraining formations on the trailing ends'and leading ends of the link are entirely clear of one another as the links go onto the sprockets, as shown clearly in FlGfl at the bottom. It is in this region that any lifting of the links above the sprocket is productive of serious problems,

7 since it is in thisregion that the chain is under high tension,

owing to the application of power from'the drive sprocket immediately ahead. In this tensioned region, therefore, there can into alignment with the departing leading link, the stop or restraining surface 34' engages on the arcuate seating surface 30', and the following link 14 is thus held down, at its forward end, by the leading link, throughout the ensuing rectilinear travel on the saw bar, not shown.

As illustrated in FIG. 5, the link tangentially leaving the sprocket has been .elevated a distance represented at d, and this rise is owing first to the link depression 14a, and second to the toe portion 40 of the trailing link 14' engaging upwardly against the toe 42' on the trailing end portion 25 of the preceding link 14'. The distance of this lift, over and above that inevitably'occurring owing to the link depression at 14a, is substantially .024 inch. Since this occurs in the region where the. chain is going off the drive sprocket, where slack tends to occur, it causes no problem and can be tolerated without penalty. There is, of course, no such rise of the links where they go onto the sprocket, for reasons described in connection withthe embodiments of FIGS. 1 and 2, i.e. since, as shown in FIG. I, the interengaging restraining formations on the links 14 are unengaged' where the chain goes onto the drive sprocket. The chain in the form of FIGS. 4 and 5 is thus deemed to have some advantage over that of FIGS. 1 and 2 in that, as previously said, the interengaging formations are stronger and more rugged, as well as being easier to manufacture. The kinematic disadvantage pointed out in the rise of the link departing from the sprocket by the amount d as shown in FIG. is of no practical disadvantage, because in this region of the chain, as earlier described, there is a certain amount of slack in the chain. and the amount of rise here involved is too insignificant to produce any objectionable vibration.

Reference is next directed to FIG. 6, showing another embodiment of the invention, using the principles set forth in connection with FIGS. l-5, but with certain variations. For convenience, parts in FIG. 6 corresponding to parts in FIGS. 1-3 will be identified by corresponding reference numerals, but the addition of double primes in FIG. 6.

In the case of FIG. 6, the leading portion 26" of each side link 14" has a toe 40", the upper surface or flank 38" of which coincides with the centerline A-A' of the chain when the links are rectilinearly aligned. The toe 42" on the trailing end portion of each side link 14" extends angularly down into the notch 36" formed between flank 38" and surface 30" on the front end of thefollowing link 14", so that its tip engages the toe 40" at the base of flank 38" when the links are rectilinearly aligned; and when the links 14" are angularly disposed relative to one another, as in going around the sprocket, the tip of the toe 42" moves outwardly along the flank 38" of the toe 40", as clearly shown in FIG. 6. 1n the latter position, as will be seen, the toe 42" holds down the following link 14" by engagement of its tip with the outer end portion of the toe flank 38", so that the links are held against outward tilting while going about the sprocket. And in the rectilinearly aligned position, as when traversing the saw bar, the tip of the toe 42" on the trailing end portion of a given link 14" holds down the forward end portion of the following link 14" by engaging the toe flank 38" near the base of the latter.

The embodiment of FIG. 6 involves a slight rise of the link 14 in leaving the sprocket at the top (not illustrated), but this rise, similar to that of the embodiments of FIGS. 4 and 5, is not appreciable, and occurring in the slack region of the chain, introduces no problem. As with the embodiments of FIGS. 1- and 4 and 5, the embodiment of FIG. 6 results in the interengaging toe members 40" and 42" disengaging from one another at the bottom of the sprocket, where the chain goes onto the sprocket, and so there is no possibility for the oncoming links to be lifted off the sprocket at the bottom by these members 40" and 42 Accordingly, the chain of FIG. 6 also runs in a kinematically correct manner, the cutter links being restrained to their predetermined positions both on the sprocket and along the saw bar, and a slight lift as the links leave the sprocket being of no consequence in view of the well known fact that there is a slight slack in the chain at this point.

It will be seen that I have provided a new form of a saw chain, having a number of features and advantages, including the advantage that the cutter links are firmly and positively held down against outward tilting about their rearward pivots along the straight runs of a saw bar, and including the further advantage that the cutter-carrying links are positively restrained to move in a path of predetermined curvature while going around the drive sprocket, with full, positive restraint against tilting outwardly about the rear pivots of the links. Sharpening to a degree of perfection not heretofore attained is thereby made possible. The chain runs with excellent stability, cuts rapidly, and vibration is controlled.

The-invcntion has now been disclosed by way of several present illustrative embodiments, it being understood, however, that numerous changes in design, structure, and arrangement may be made without departing from the scope of the invention. The modifications which can be made in the invention, of course, include that in which the interengaging tiltrestraining formations are used between successive center links, and it is thus to be understood that, broadly speaking, whether the drive roots are used on the center links or the side links and whether the inter-engaging tilt-restraining formations are used on the side links or on the center links, is to a large 'extent a matter of choice and design, it being further understood that large leeway is left for use of cutters of various types on either the side links and/or the center links, as desired.

It is claimed:

1. A saw chain comprising:

a succession .of links;

pivots connecting said links end to end;

cutters on certain of said links;

sprocket drive roots on certain of said links;

a sprocket for moving said links in a curved path between two longitudinal runs of the chain; and

alternate links of said succession having leading and trailing ends including front and rear extensions extending generally longitudinally of the links beyond the corresponding connecting pivots, the rear extension of a given one of said alternate links having a stop element that overlies a formation on the front extension of the following alternate-link, said stop element and said formation being positioned to positively engage one another when said leading and immediately following links of said alternate links and the link intervening therebetwcen are in an acute exterior angle orientation relative to one another in conformance with said curved path, and said stop element and said front extension being formed and positioned, to be free of one another when said given link is angularly related to said intervening link and said immediately following link is substantially rectilinearly aligned with said intervening link.

2. The subject matter of claim I, wherein said rear longitudinal extension is formed on its inner side with a generally transverse notch,.the rearward flank of which has said stop element thereon, and said front longitudinal extension is formed with a nose portion adapted to enter said notch and having thereon said formation engageable with said stop element on said rearward flank of said notch when said links are in said acute exterior angle orientation.

3. The subject matter of claim 1, wherein said rear longitudinal extension projects from the transversely outer portion of said leading link and is formed on its inner side with a generally transverse notch, the rearward flank of which has said stop element thereon, and said front longitudinal extension projects from the transversely inner portion of said following link and is formed with a nose portion adapted to enter said notch and having thereon said formation engageable with said stop element on said rearward flank of said notch when said links are in said acute exterior angle orientation.

4. The subject matter of claim 3, wherein the rearward flank of said notch is formed on an arc struck about the center of the rear pivot of said leading link, and said nose portion of said front extension of said following link has a rearward flank formed on an are also struck about the center of the rear pivot of said leading link;

5. The subject matter of claim 2, wherein the forward end of said following link has a convex, substantially arcuate, outwardly and forwardly facing surface, and said rear extension of said leading link has a concave, substantially arcuate surface overlying and engageable against said convex surface when said leading and following links and said intervening link are rectilinearly aligned.

6. The subject matter of claim 5, wherein said convex surface on the forward end of the following link merges into a surface forming one side of a notch extending inwardly of a centerline defined by the pivots of said link, and theother side of which forms the rearward flank of said nose portion, the extremity of said nose portion being located substantially in the region of said centerline of said link, and said extremity and said flank of said nose portion being out of engagement with said rearward flank of said notch in said rear extension of said leading link when said links are rectilinearly aligned.

7. The subject matter of claim 1, wherein said rear and front longitudinal extensions overlap one another longitudinally, with said rear extension lying transversely outward of said front extension, said extensions having confronting configurations which engage one another near the extremity of the rearward extension and the base of the front extension when the links are rectilinearly aligned, at said stop element at an intermediate point along the rear extension and at the extremity of the front extension when the links are at acute angles to one another, and which are clear of one another when the leading link and the intervening link are at an angle to one another and the following link is substantially rectilinearly aligned with the intervening link.

disposed substantially parallel to the centerline of the following link defined by the centers of the pivots thereof, and a substantially transversely inwardly facing surface on said rear extension formed with an inward incline in the direction toward the extremity of said rear extension.

10. The subject matter of claim 1, wherein the forward end of said following link has a convex, arcuate surface, struck from a center at the rear pivot of said link, facing generally outwardly and forwardly of said link, and said rear and front longitudinal extensions overlap one another longitudinally, with said rear extension lying transversely outward of said front extension, said extensions having confronting configurations which engage one another at said stop element on said rear extension and at said formation on said rear extension when the links are at acute exterior angles to one another, and

which are clear of one another when the leading link and the ing link, said rear extension having a stop element which engages said convex arcuate surface on the forward end of the following link when said links are angularly related to one another in said curved path.

11. The subject matter of claim 1, wherein said cutters are on said alternate links.

12. The subject matter of claim 3, wherein said cutters are 'on said alternate links.

13. The subject matter of claim 8, wherein said cutters are on said alternate links.

14. The subject matter of claim 11, wherein said alternate links comprise pairs of side links, and the remaining links comprise center links.

15. The subject matter of claim 12, wherein said alternate links comprise pairs of side links, and the remaining links comprise center links. I

' 16 The subject matter of claim 13, wherein said alternate links comprise pairs of side links, and the remaining links comprise center links. 

